The present invention relates to a control system for a vehicle, which influences at least one quantity representing tire slip.
A vehicle dynamics control system is discussed in SAE paper 950759, which is entitled xe2x80x9cVDC, The Vehicle Dynamics Control System of Boschxe2x80x9d by Anton T. van Zanten, Rainer Erhardt and Georg Pfaff. The control system includes an anti-lock controller, a traction controller, an engine drag torque controller, and a controller that operates based on a quantity representing the yaw rate of the vehicle. These control systems are implemented in a control unit, which influences the braking system of the vehicle, and which, via a communication connection, is connected to a control unit for controlling a drive unit, such as the engine and/or the transmission. This control system may include relatively complex software and hardware because of, for example, computer performance requirements, the required transmission rate requirements between control systems or other considerations.
European Patent No. EP 0 386 126 concerns a traction controller, in which a slippage of at least one drive wheel is detected and an engine torque is reduced based on the slippage, particularly when the slippage exceeds a preset threshold value. When the slippage is adjusted to such a preset value or range, the engine torque is slowly increased (or ramped up) by controlling correspondingly the throttle valve according to a predefined procedure. This reference, however, does not describe a procedure for determining the magnitude of the reduction of the engine torque if there is unacceptable slippage.
Non-prepublished German Patent Application No. 198 44 912.7 concerns a control system for a vehicle, in which a transverse acceleration acting upon the vehicle is detected, and a time response of the transverse acceleration is determined. The power output or the torque of the vehicle""s drive unit is influenced based on these two quantities. In the case of the drive unit, this procedure should ensure a stable vehicle behavior, particularly when cornering.
An object of an exemplary embodiment of the present invention is to provide a control system that influences a drive unit of the vehicle at least for controlling a slip quantity, but which has a reduced degree of complexity in its software and hardware and still provides satisfactory control response.
Another object of an exemplary embodiment of the present invention is to provide an implementation of an effective, relatively simple traction controller in a control unit that influences the torque of the vehicle""s drive unit. Such an implementation should simplify the software and hardware requirements (such as, the ROM requirement). It is believed that it may be particularly advantageous to combine this traction controller with the transverse acceleration control system discussed in the Background Information, and provide a drive dynamics control system which, in the case of the drive input, improves vehicle stability. By implementing this simpler, reduced outlay system in the control unit for the drive unit of the vehicle, a marked reduction of the outlay of software and hardware should be achieved without having to expect losses with respect to the vehicle""s driving stability and/or the traction of the vehicle.
It is also believed that it may be particularly advantageous to provide the traction control system with characteristic curves or maps so that setpoint values may be derived for at least one manipulated (or regulated) variable (or quantity) that controls the power output or the torque of the drive unit, such as, for example, as a function of the tire slip and/or the timerelated change in the tire slip, as well as a quantity representing the vehicular velocity. By using this relatively simple traction control system, which should reduce the outlay for the control unit, satisfactory traction control improvements may be achieved.
It is also believed that it may be particularly advantageous that the gradient (or rate of change), which is used to approximate the manipulated (or regulated) variable (or quantity) to the value corresponding to the operating state, may be weighted via the number of control cycles or via the magnitude of the slippage. It may be particularly expedient to consider slippage and slip gradient in determining the gradient. In this manner, the rapidness of approximation becomes dependent on the slip condition.
When selecting a throttle valve setpoint angle as a manipulated variable, the selected setpoint or limiting angle may be expediently corrected so that tractive resistances, such as grades (for example, uphill) and/or low engine power output at higher altitude above sea level, are taken into account, and the adjusted limiting angle permits the torque or the power output of the drive unit, even xe2x80x9coutsidexe2x80x9d of standard conditions, along the lines or in the sense of a slip reduction or of adjusting a slip control valve to a desired value.
It is also believed that it may be particularly advantageous that, during unusual operating states in which a permanent deviation occurs (such as, for example, permanent deviation of the slippage from the preset value or range of values), the deviation may be integrated, and the value that is ascertained or determined from the characteristic map or maps for the manipulated variable may be influenced as a function of the integration value so that the permanent deviation disappears. Thus, a satisfactory traction may result in exceptional situations.